Multi-carrier signal radio technique such as Orthogonal Frequency Division Multiplexing (OFDM) radio technique is generally used for transmitting quite a lot of data via various frequencies. OFDM can be used in digital broadcasting systems such as DVB system. Environments and situations in the multi-carrier signal systems like broadcasting, which itself has a long history in television and radio even as a digitalised one, have clearly created a need for evaluating the multi-carrier signal technique in a situation where it was not originally designed. An example of this kind of situation can be a mobile reception. Thus, the OFDM radio technique is facing a rising mobility challenge.
An example of a problem in the RF world can be frequency offset. When receiving such a signal, the carrier center frequency may be offset from the normal channel raster. The offset may be up to 0.5 MHz. Known ways, receivers, receiver chips or devices are only capable of synchronizing into signals with a limited maximum offset. Typically, this maximum offset is about 130 kHz. Therefore, channel search has to be performed with several offsets for every channel.
Such a known synchronization and channel search/tuning can be based on the following. During channel search, the RF demodulator scans over the nominal carrier frequency with a step of about 125 kHz. Thus, with four steps (fc−0.375 MHz, fc−0.125 MHz, fc+0.125 MHz, fc+0.375 MHz) the whole possible range is covered.
This is a very time consuming known solution. In particular, every channel search for a given frequency offset can take up to some seconds. Thus, synchronisation is too much time consuming for a mobile reception.